This invention relates to equipment and methods for detecting the presence of, measuring the amount of, and/or monitoring the level of one or more selected components in a liquid mixture.
While use may be made of this invention in chemical industry, especially where complex mixtures are encountered (e.g. in food chemistry or biochemical engineering) it is of particular value in biological investigation and control techniques. More particularly, it lends itself to animal or human medicine, and in particular to in vivo measuring or monitoring of components in body fluids.
For convenience, the invention will be described with reference primarily to one such procedure, the determination of glucose in a diabetic human subject, by the use of equipment which, while usable on a specific or occasional basis also lends itself to temporary or permanent implantation. However, while the provision of an implantable glucose sensor is a major object of the invention other and broader objects are not hereby excluded.
In vivo glucose sensors have already been proposed. One proposal is based on direct oxidation of glucose at a catalytic platinum electrode (see Hormone and Metabolic Research, Supplement Series No. 8, pp 10-12 (1979)) but suffers from the drawback of being nonspecific and of being easily poisoned by interfering substances. Another proposal, for a procedure more specific to glucose, involves the use of glucose oxidase on an oxygen electrode (Adv. Exp. Med. Biol, 50 pp 189-197 (1974)) but is not very responsive to the high glucose concentrations. Other systems using glucose oxidase have been proposed but not fully investigated for in vivo methods, see e.g. J. Solid-Phase Biochem. 4 pp 253-262 (1979).
The inventors have recently carried out in vitro studies of enzyme-catalysed reactions using a mediator in solution to transfer the electrons arising from the enzyme, during its action, directly to the electrode, as described in Biotechnology Letters 3 pp 187-192 (1981).